Semiconductor light emitting diodes having reflective structures and methods of fabricating same

ABSTRACT

Light emitting diodes include a diode region having first and second opposing faces that include therein an n-type layer and a p-type layer, an anode contact that ohmically contacts the p-type layer and extends on the first face, and a cathode contact that ohmically contacts the n-type layer and also extends on the first face. The anode contact and/or the cathode contact may further provide a hybrid reflective structure on the first face that is configured to reflect substantially all light that emerges from the first face back into the first face. Related fabrication methods are also described.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation-in-part application of U.S.application Ser. No. 11/985,410, entitled “Wire Bond Free Wafer LevelLED” filed Nov. 14, 2007, and U.S. application Ser. No. 12/329,713,entitled “Light Emitting Diode With Improved Light Extraction”, filedDec. 8, 2008, the disclosures of both of which are hereby incorporatedherein by reference as if set forth in their entirety herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was developed with Government support underContract No. 70NANB4H3037 of the Department of Commerce. The Governmenthas certain rights in this invention.

BACKGROUND OF THE INVENTION

This invention relates to semiconductor light emitting devices andmethods of fabricating same, and more particularly to semiconductorLight Emitting Diodes (LEDs) and fabrication methods therefor.

Semiconductor LEDs are widely known solid-state lighting elements thatare capable of generating light upon application of voltage thereto.LEDs generally include a diode region having first and second opposingfaces, and including therein an n-type layer, a p-type layer and a p-njunction. An anode contact ohmically contacts the p-type layer and acathode contact ohmically contacts the n-type layer. The diode regionmay be epitaxially formed on a substrate, such as a sapphire, silicon,silicon carbide, gallium arsenide, gallium nitride, etc., growthsubstrate, but the completed device may not include a substrate. Thediode region may be fabricated, for example, from silicon carbide,gallium nitride, gallium phosphide, aluminum nitride and/or galliumarsenide-based materials and/or from organic semiconductor-basedmaterials. Finally, the light radiated by the LED may be in the visibleor ultraviolet (UV) regions, and the LED may incorporate wavelengthconversion material such as phosphor.

LEDs are increasingly being used in lighting/illumination applications,with one ultimate goal being a replacement for the ubiquitousincandescent lightbulb.

SUMMARY OF THE INVENTION

Light emitting diodes according to various embodiments include a dioderegion having first and second opposing races and including therein ann-type layer and a p-type layer, an anode contact that ohmicallycontacts the p-type layer and extends on the first face and a cathodecontact that ohmically contacts the n-type layer and also extends on thefirst face. The anode contact and/or the cathode contact further includea reflective structure on the first face that is configured to reflectsubstantially all light that emerges from the first face back into thefirst face. In some embodiments, the reflective structure reflects thelight that emerges from at least 90% of an area of the first face backinto the first face. Moreover, the reflective structure itself may beconfigured to reflect at least 90% of the light that impinges thereon.Accordingly, embodiments of the present invention can provide laterallight emitting diodes having both contacts on a given face thereof andan integral reflective structure. The lateral light emitting diodes maybe used in a flip-chip configuration, such that the contacts may be usedto mount the LED on a packaging substrate, and the light emerges fromthe light emitting diode from a face other than the first face.

In some embodiments, the reflective structure comprises a reflectivesurface of the anode contact that ohmically contacts the p-type layer, areflective surface of the cathode contact, and a reflective surface ofan extension of the cathode contact. The reflective structure furtherincludes a transparent insulating layer beneath the cathode contact andits extension. In some of these embodiments, a barrier layer may beprovided on the anode contact including on sidewalls thereof, and thereflective structure can reflect all the light that emerges from thefirst face back into the first face, except for light that is absorbedby the barrier layer on the sidewalls of the anode contact. In otherembodiments, the anode contact is transparent, and the reflectivestructure further comprises a reflective surface of an extension of thecathode contact that extends onto the transparent anode contact. Thetransparent insulating layer also may extend beneath the extension ofthe cathode content that is on the transparent anode contact. In some ofthese embodiments, a current spreading layer may be provided on thetransparent anode contact and the reflective structure can reflect allthe light that emerges from the first face back into the first face,except for light that is absorbed by the current spreading layer.

A transparent substrate may be provided on a second face in any of theseembodiments, so that the light emerges from the transparent substrate.The transparent substrate can include an outer face that is remote fromthe diode region, and the outer face can be differently textured in afirst portion thereof than a second portion thereof, so as to provide anorientation indicator for the light emitting diode.

In other embodiments, an anode pad is electrically connected to theanode contact and a cathode pad is electrically connected to thereflective cathode contact. The anode and the cathode pad extend on thefirst face in closely spaced apart relation to one another, to define agap therebetween. Moreover, in some embodiments, the light emittingdiode is flip-chip mounted on a mounting substrate, such that the anodeand cathode pads are adjacent the mounting substrate, and the dioderegion is remote from the mounting substrate.

Light emitting diodes according to other embodiments comprise a dioderegion including therein an n-type layer and a p-type layer, and acontact for one of the n-type layer or the p-type layer. The contactincludes a transparent insulating layer on one of the n-type layer orthe p-type layer that has an index of refraction that is less than theone of the n-type layer or the p-type layer. A reflective layerelectrically contacts the one of the n-type layer or the p-type layer,and extends on the transparent insulating layer. In some embodiments,the reflective layer electrically contacts the one of the n-type layeror the p-type layer by extending through the transparent insulatinglayer and extending on the transparent insulating layer. In otherembodiments, the reflective layer ohmically contacts the one of then-type layer or the p-type layer. The transparent insulating layer andthe reflective layer can provide a hybrid reflective structure or“hybrid mirror”, wherein the underlying transparent insulating layerprovides an index of refraction mismatch or index step to enhance thetotal internal reflection (TIR) from the diode region compared toabsence of the underlying transparent insulating layer.

In still other embodiments, the contact is a first contact and thereflective layer is a first reflective layer, and the light emittingdiode further includes a second contact for the other of the n-typelayer or the p-type layer. The second contact comprises a secondreflective layer that ohmically contacts the other of the n-type layeror the p-type layer. In still other embodiments, a second contact forthe other of the n-type layer or the p-type layer comprises atransparent conductive layer that ohmically contacts the other of then-type layer or the p-type layer, and the transparent insulating layerand the reflective layer both extend onto the transparent conductivelayer. In some embodiments, the transparent conductive layer has anindex of refraction between that of the other of the n-type layer or thep-type layer and the transparent insulating layer. Moreover, in any ofthese embodiments, the first and second contacts can both extend from onthe first face of the diode region and a transparent substrate can beprovided on the second face that has an index of refraction that isabout the same as the diode region. The substrate can thereby enhancelight extraction.

Light emitting diodes according to still other embodiments include adiode region having first and second opposing faces and including ann-type layer and a p-type layer. A reflective anode contact ohmicallycontacts the p-type layer and extends on the first face. A reflectivecathode contact also ohmically contacts the n-type layer and extends onthe first face. The reflective anode contact and the reflective cathodecontact are configured to collectively reflect substantially all lightthat emerges from the first face back into the first face. Thereflective anode contact may comprise a reflective layer and a barrierlayer as described above. In other embodiments, the reflective cathodecontact may comprise a transparent insulating layer and a reflectivelayer, as described above.

Light emitting diodes according to yet other embodiments include a dioderegion having first and second opposing faces and including therein ann-type layer and a p-type layer. An anode contact ohmically contacts thep-type layer and extends on the first face. A transparent insulatinglayer extends on the first face outside the anode contact. A reflectivecathode contact electrically contacts the n-type layer and extendsthrough the transparent insulating layer and onto the transparentinsulating layer that is outside the anode contact, to coversubstantially all of the first face that is outside the anode contactwith the reflective cathode contact. In some embodiments, thetransparent insulating layer also extends onto the anode contact and thereflective cathode contact also extends onto the transparent insulatinglayer that is on the anode contact, to cover substantially all of thefirst face that is outside the anode contact with the reflective cathodecontact and to also cover at least a portion of the anode contact withthe reflective cathode contact. Moreover, some embodiments include a viathat extends into the first face to expose the n-type layer and thetransparent insulating layer extends into the via. The reflectivecathode contact also extends on the transparent insulating layer intothe via to electrically contact the n-type layer that is exposed in thevia. The transparent insulating layer and the reflective layer canprovide a hybrid reflective structure or “hybrid mirror”, wherein theunderlying transparent insulating layer provides an index of refractionmismatch or index step to enhance the TIR from the diode region comparedto absence of the underlying transparent insulating layer.

In some embodiments, the reflective cathode contact directly ohmicallycontacts the n-type layer. However, in other embodiments, an ohmiccontact is provided that directly ohmically contacts the n-type layerand the reflective cathode contact is on the ohmic contact. Moreover, insome embodiments, the transparent insulating layer may comprise aplurality of transparent sublayers to provide, for example, adistributed Bragg reflector and/or the reflective layer may include aplurality of sublayers.

Some embodiments include a reflective anode contact, whereas otherembodiments include a transparent anode contact. Thus, in someembodiments, the anode contact comprises a reflective anode contact thatohmically contacts the p-type layer and extends on the first face. Thereflective anode contact may include sidewalls, and the light emittingdiode may further comprise a barrier layer on the reflective anodecontact, including on the sidewalls thereof.

In other embodiments, the anode contact comprises a transparent anodecontact that ohmically contacts the p-type layer and extends on thefirst face. A current spreading layer may also be provided on a portionof the transparent anode contact. The transparent insulating layer mayextend onto the transparent anode contact and the reflective cathodecontact may also extend onto the transparent insulating layer that is onthe transparent anode contact, to cover at least a portion of thetransparent anode contact with the reflective cathode contact. Moreover,where a current spreading layer is present on a portion of thetransparent anode contact, the transparent insulating layer may extendonto the transparent anode contact that is outside the portion and thereflective cathode contact may also extend onto the transparentinsulating layer that is on the transparent anode contact outside theportion, to cover the transparent anode contact that is outside theportion with the reflective cathode contact.

Any of the above-described embodiments may include an anode pad that iselectrically connected to the anode contact and a cathode pad that iselectrically connected to the reflective cathode contact. The anode andcathode pads may extend on the first face in closely spaced apartrelation to one another to define a gap therebetween. In someembodiments, the anode pad and the cathode pad both extend on thereflective anode contact and the reflective anode contact includes abreak therein that corresponds to the gap, so as to allow the cathodeand anode pads to be electrically insulated from one another. In theseembodiments, the light emitting diode may further include a reflectivelayer that is insulated from the anode pad and/or the cathode pad, andthat extends across the break. Moreover, in some embodiments, thereflective cathode contact also provides a plating seed layer, and theanode and cathode pads are plated anode and cathode pads on the seedlayer. In other embodiments, a separate plating seed layer may beprovided. In still other embodiments, the light emitting diode isflip-chip mounted on the mounting substrate such that the anode andcathode pads are adjacent the mounting substrate and the diode region isremote from the mounting substrate.

In other embodiments, a transparent substrate may be included on thesecond face. The transparent substrate may include an outer face that isremote from the diode region. The transparent substrate can enhancelight extraction. The outer face can be differently textured in a firstportion thereof than a second portion thereof, so as to provide anorientation indicator for the light emitting diode. In still otherembodiments, a substrate is not included, and the second opposing faceof the diode region may be textured, with or without the orientationindicator.

Light emitting diodes according to still other embodiments include adiode region having first and second opposing faces, and includingtherein an n-type layer and a p-type layer. A transparent anode contactohmically contacts the p-type layer and extends on the first face. Atransparent cathode contact ohmically contacts the n-type layer and alsoextends on the first face. A transparent insulating layer extends on thefirst face including on the transparent anode contact and thetransparent cathode contact. A reflective layer is provided on thetransparent insulating layer that substantially covers the first face.The transparent insulating layer and the reflective layer can provide ahybrid reflective structure or “hybrid mirror”, wherein the underlyingtransparent insulating layer provides an index of refraction mismatch orindex step to enhance the TIR from the diode region compared to absenceof the underlying transparent insulating layer.

In some embodiments, a current spreading layer may be provided betweenthe transparent anode contact and the reflective layer and between thetransparent cathode contact and the reflective layer. In someembodiments, the reflective layer includes first and second portions,and the current spreading layer electrically connects the transparentanode contact to the first portion and electrically connects thetransparent cathode contact to the second portion. Moreover, in otherembodiments, the transparent anode contact and the transparent cathodecontact both comprise transparent conductive metal oxide, such as indiumtin oxide. The reflective layer comprises an elemental metal layer thatis spaced apart from the first face, such that the first face is free ofdirect contact with elemental metal.

As to other materials, in some embodiments, the diode region comprises aGroup III-nitride, such as gallium nitride-based material. Thetransparent insulating material comprises silicon dioxide, and thereflective cathode contact comprises aluminum. The reflective anodecontact comprises nickel and silver. The transparent anode contactcomprises indium tin oxide. Moreover, the transparent substratecomprises silicon carbide. Other materials may be used in otherembodiments.

Methods of fabricating light emitting diodes also may be providedaccording to other embodiments. In some embodiments, a via is etchedthrough a p-type layer at a first face of a diode region to expose ann-type layer therein. An anode contact is formed on the first face thatohmically contacts the p-type layer. A transparent insulating layer isformed on sidewalls of the via and extending onto the first face outsidethe via. A reflective cathode contact is formed that ohmically contactsthe n-type layer on a floor of the via and that extends on thetransparent layer that is on the sidewalls of the via and on thetransparent layer that is on the first face outside the via.

More specifically, the anode contact may be formed by forming atransparent anode contact that ohmically contacts the p-type layer andextends on the first face. A current spreading layer may then be formedon a portion of the transparent anode contact. Moreover, the transparentinsulating layer may be formed to extend on the transparent anodecontact, and the reflective cathode contact may also extend on thetransparent insulating layer that is on the transparent anode contact.In other embodiments, the anode contact may be fabricated by forming areflective layer that ohmically contacts the p-type layer and forming abarrier layer on the reflective layer including on the sidewallsthereof. Moreover, the transparent insulating layer may be formed byblanket forming a transparent insulating layer and opening vias in thetransparent insulating layer that extend to the n-type layer and thep-type layer. Analogous methods may be provided to fabricate the otherembodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are cross-sectional views of light emitting diodes accordingto various embodiments.

FIGS. 5A-5B are top views of light emitting diodes according to variousembodiments.

FIG. 6 is a flowchart of operations that may be performed to fabricatelight emitting diodes according to various embodiments.

FIG. 7A is a top view and FIG. 7B is a cross-sectional view along line7B-7B′ of FIG. 7A, of a light emitting diode according to various otherembodiments.

FIGS. 8A-8C are cross-sectional views of light emitting diodes of FIGS.7A and 7B during intermediate fabrication steps according to otherembodiments.

FIG. 9 is a cross-sectional view of a light emitting diode according toyet other embodiments.

FIGS. 10A-10D and 10A′-10D′ are cross-sectional and top plan views,respectively, of light emitting diodes according to various embodimentsduring fabrication according to various embodiments.

FIG. 11 is a plan view of an alternate embodiment of FIG. 10D′

FIG. 12 is a cross-sectional view of a light emitting diode according toembodiments of FIG. 3, mounted on a mounting substrate in a flip-chipconfiguration according to various embodiments.

DETAILED DESCRIPTION

The present invention now will be described more fully with reference tothe accompanying drawings, in which various embodiments are shown. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the size and relative sizes oflayers and regions may be exaggerated for clarity. Like numbers refer tolike elements throughout.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. Furthermore, relative terms such as “beneath” or “overlies” maybe used herein to describe a relationship of one layer or region toanother layer or region relative to a substrate or base layer asillustrated in the figures. It will be understood that these terms areintended to encompass different orientations of the device in additionto the orientation depicted in the figures. Finally, the term “directly”means that there are no intervening elements. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items and may be abbreviated as “/”.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

Embodiments of the invention are described herein with reference tocross-sectional and/or other illustrations that are schematicillustrations of idealized embodiments of the invention. As such,variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the invention should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, a region illustrated or described as arectangle will, typically, have rounded or curved features due to normalmanufacturing tolerances. Thus, the regions illustrated in the figuresare schematic in nature and their shapes are not intended to illustratethe precise shape of a region of a device and are not intended to limitthe scope of the invention, unless otherwise defined herein.

Unless otherwise defined herein, all terms (including technical andscientific terms) used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand this specification and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

As used herein, a layer or region of an LED is considered to be“transparent” when at least 90% of the radiation from the LED thatimpinges on the transparent layer or region emerges through thetransparent region. For example, in the context of blue and/or greenLEDs that are fabricated from gallium nitride-based materials, silicondioxide can provide a transparent insulating layer (for example, atleast 90% transparent), whereas indium tin oxide (ITO) can provide atransparent conductive layer (for example, at least 90% transparent) asmeasured by considering transmitted and reflected components on asapphire substrate. Moreover, as used herein, a layer or region of anLED is considered to be “reflective” when at least 90% of the angleaveraged radiation that impinges on the reflective layer or region fromthe LED is reflected back into the LED. For example, in the context ofgallium nitride-based blue and/or green LEDs, aluminum (for example, atleast 90% reflective) may be considered reflective materials. In thecase of ultraviolet (UV) LEDs, appropriate materials may be selected toprovide a desired, and in some embodiments high, reflectivity and/or adesired, and in some embodiments low, absorption.

Some embodiments now will be described generally with reference togallium nitride (GaN)-based light emitting diodes on silicon carbide(SiC)-based mounting substrates for ease of understanding thedescription herein. However, it will be understood by those having skillin the art that other embodiments of the present invention may be basedon a variety of different combinations of mounting substrate andepitaxial layers. For example, combinations can include AlGaInP diodeson GaP mounting substrates; InGaAs diodes on GaAs mounting substrates;AlGaAs diodes on GaAs mounting substrates; SiC diodes on SiC or sapphire(Al₂O₃) mounting substrates and/or a Group III-nitride-based diode ongallium nitride, silicon carbide, aluminum nitride, sapphire, zinc oxideand/or other mounting substrates. Moreover, in other embodiments, amounting substrate may not be present in the finished product. In someembodiments, the light emitting diodes may be gallium nitride-based LEDdevices manufactured and sold by Cree, Inc. of Durham, N.C.

FIG. 1 is a cross-sectional view of a light emitting diode according tovarious embodiments. Referring to FIG. 1, these light emitting diodesinclude a diode region 110 having first and second opposing faces 110 a,110 b, respectively, and including therein an n-type layer 112 and ap-type layer 114. Other layers or regions 116 may be provided which mayinclude quantum wells, buffer layers, etc., that need not be describedherein. The diode region 110 also may be referred to herein as an “LEDepi region”, because it is typically formed epitaxially on a substrate120. For example, a Group III-nitride based LED epi 110 may be formed ona silicon carbide growth substrate 120. In some embodiments, as will bedescribed below, the growth substrate 120 may be present in the finishedproduct. In other embodiments, the growth substrate 120 may be removed.

Continuing with the description of FIG. 1, an anode contact 130, alsoreferred to as a “p-contact”, ohmically contacts the p-type layer 114and extends on the first face 110 a of the diode region 110. The anodecontact 130 may extend to a greater or less extent on the p-type layer114 than illustrated in FIG. 1. A transparent insulating layer 140 alsoextends on the first face 110 a outside the anode contact 130. Areflective cathode contact 150, also referred to as an “n-contact”electrically contacts the n-type layer 112 and extends through thetransparent insulating layer 140 and onto the transparent insulatinglayer 140 that is outside the anode contact 130. In some embodiments,the reflective cathode contact 150 may directly and ohmically contactthe n-type layer 112. In other embodiments, however, a thin ohmiccontact layer, such as a layer of titanium, may provide the actual ohmiccontact to the n-type layer 112. The transparent insulating layer 140and the reflective cathode contact 150 can provide a hybrid reflectivestructure or “hybrid mirror”, wherein the underlying transparentinsulating layer 140 provides an index refraction mismatch or index stepto enhance the total internal reflection (TIR) from the reflective layer150 compared to absence of the underlying transparent insulating layer140. It will also be understood that, in other embodiments, thetransparent insulating layer 140 may comprise multiple sublayers, suchas oxide and nitride sublayers to provide, for example, a distributedBragg reflector. Moreover, the reflective cathode contact 150 may alsoinclude a plurality of sublayers.

As also shown in FIG. 1, in some embodiments, a via 118 extends into thefirst face 110 a to expose the n-type layer 112, and the transparentinsulating layer 140 extends into the via 118. Moreover, the reflectivecathode contact 150 also extends on the transparent insulating layer 140into the via 118, to electrically, and in some embodiments ohmically,contact the n-type layer 112 that is exposed in the via 118.

An anode pad 160 also is provided that is electrically connected to theanode contact 130. A cathode pad 170 is also provided that iselectrically connected to the reflective cathode contact 150. As shown,the anode and contact pads 160 and 170 extend on the first face 110 a inclosely spaced apart relation to one another, to define a gap 172therebetween. The gap may be filled with an insulator as describedbelow. In any embodiments illustrated herein, the gap 172 may occur atany desired position and is not limited to the position illustratedherein. In some embodiments, the cathode pad 170 may be made as large aspossible, so that it can be directly coupled to a grounded heat sink forenhanced thermal dissipation in a flip-chip mounting configuration,without the need for an intervening electrically insulating layer thatcould reduce thermal efficiency.

As also shown in FIG. 1, a transparent substrate, such as a transparentsilicon carbide growth substrate 120, may be included on the second face110 b of the diode region 110. The transparent substrate 120 may includebeveled sidewalls 120 a and may also include an outer face 120 b that isremote from the diode region 110. As shown, the outer face 120 b may betextured. The thickness of the substrate 120, the resistivity of thesubstrate, geometry of the sidewalls 120 a and/or the texturing of theremote face 120 b may be configured to enhance the far field emission ofradiation from the diode region 110 through the substrate 120. Theemission from the diode region 110 may take place directly from thediode region 110 through the substrate 120 and may also take place byreflection from the reflective cathode contact 150 back through thediode region 110 and through the substrate 120. In some embodiments,reflection may also take place from the anode contact 130, as will bedescribed in detail below.

As also shown in FIG. 1, in some embodiments, when the transparentsubstrate 120 is sapphire, Patterned Sapphire Substrate (PSS) technologymay be used to texture the interface between the sapphire substrate 120and the diode region 110, as shown by the jagged interface between thesubstrate 120 and the second face 110 b of the diode region 110. As iswell known, PSS technology may provide texture features that may be, forexample, about 3 μm in size on an about 5 μm pitch. The use of PSStechnology can enhance the extraction efficiency between the galliumnitride-based diode region 110 and the index mismatched sapphiresubstrate 120.

Accordingly, some embodiments of the invention can provide an LED thatis suitable for flip-chip mounting (i.e., mounting opposite theorientation of FIG. 1), wherein the anode pad 160 and the cathode pad170 are mounted on a supporting substrate, such as a printed circuitboard or other wiring board, and emission of light takes place throughthe substrate 120 remote from the anode pad 160 and the cathode pad 170.Thus, a lateral LED may be provided wherein both the anode contact 130and the cathode contact 150 extend on a given face of the diode region(i.e., the first face 110 a), and emission takes place remote from theanode and cathode contacts 130 and 150, respectively, through the secondface 110 b of the diode region, and through the substrate 120. In otherembodiments, the substrate may be removed so that emission takes placedirectly from the second face 110 b of the diode region 110.

As was noted above, the geometry of the substrate 120 may be configuredto provide a desired far field emission pattern, such as Lambertianemission. Moreover, texturing may take place on the sidewalls 120 aand/or on the face 120 b of the substrate 120. Many differentconfigurations of texturing may be used including random texturing,microlenses, microarrays, scattering regions and/or other opticalregions. According to some embodiments, the outer face 120 b may bedifferently textured in a first portion 120 c thereof than a secondportion 120 d thereof, so as to provide an orientation indicator for thelight emitting diode. Thus, as shown in FIG. 1, an array of microlenses120 d may be provided except at a given area adjacent the transparentcathode contact, wherein a small bar 120 c or other indicator, such as a“+” sign, may be provided. The different texturing on the remote face120 b of the substrate can provide an orientation indicator that canallow pick-and-place equipment to correctly orient the LED forpackaging, even if the structure of the LED is not “visible” to thepick-and-place equipment through the textured substrate.

In some embodiments, the anode contact and/or the cathode contact canprovide a reflective structure on the first face 110 a that isconfigured to reflect substantially all light that emerges from thefirst face 110 a back into the first face 110 a. The reflectivestructure further includes the transparent insulating layer 140 beneaththe cathode contact 150 and extensions thereof 150 a. In particular, insome embodiments, the reflective structure reflects the light thatemerges from at least 90% of an area of the first face 110 a. Thereflective structure may comprise reflective materials that themselvesreflect at least 90% of the light that impinges thereon. In someembodiments, the anode contact 130 may be a reflective anode contactthat ohmically contacts the p-type layer 114. In these embodiments, thereflective structure may be provided by a reflective surface of theanode contact 130 that ohmically contacts the p-type layer 114, areflective surface of the cathode contact 150 that ohmically contactsthe n-type layer 112 and a reflective surface of extensions of thecathode contact, identified as 150 a in FIG. 1, that extend onto thefirst face 110 a between the via 118 and the anode contact 130, incombination with the transparent insulating layer 140. In otherembodiments, the anode contact 130, may be transparent, and thereflective cathode contact 150, specifically the extensions 150 a of thereflective cathode contact 150, may extend onto the transparent anodecontact 130 to provide a reflective structure in combination with thetransparent insulating layer 140. Thus, in some embodiments, thereflective cathode contact can extend to cover substantially all of thefirst face that is outside the anode contact with the reflective cathodecontact. In other embodiments, the reflective cathode contact can coversubstantially all of the first face that is outside the anode contactwith the reflective cathode contact, and also can cover at least aportion of the anode contact with the reflective cathode contact. Moredetailed embodiments will be described below.

Accordingly, some embodiments may provide LEDs with a lateral flip-chipconfiguration. Some embodiments may provide dual mirrors on the p-typeand n-type layers. Moreover, the n-type mirror may be an integratedn-contact mirror that can make electrical contact with at least onen-type layer of the LED epi, and can also extend over at least onep-type contact of the LED epi. The integrated n-contact mirror mayinclude a material, such as aluminum, that is optically reflective towavelengths generated by the LED epi. The transparent insulating layerand the reflective layer can provide a hybrid reflective structure or“hybrid mirror”, wherein the underlying transparent insulating layerprovides an index of refraction mismatch or index step to enhance theTIR from the diode region compared to absence of the underlyingtransparent insulating layer. Moreover, the light emitting face of theLED chip, opposite the mirror(s), may include a growth substrate. Thegrowth substrate may further include a shaped surface, such as taperedsidewalls and/or texturing, for light extraction purposes. The amount oftapering and/or texturing may be related to the total thickness of theLED, including the growth substrate. The geometry of the substrate(e.g., thickness/sidewall bevels) and/or the texturing thereof may beadjusted to achieve desired far-field emission patterns. Moreover, sincethe substrate need not conduct current, it can have high resistivity sothat it can be transparent.

LED chips according to various embodiments may be more rugged or robustthan conventional LED chips. In particular, the only exposed surfaces ofthe LED chip may be solid p- or n-contact portions on one side, and thegrowth substrate on the other side. In contrast, conventional LED chipsmay need fragile wire bonds and may include exposed top and/or bottomportions of the LED epi.

Moreover, it has also been found, according to various embodiments, thatthe provision of a transparent insulating layer between the diode regionand the reflective cathode contact may actually enhance the reflectivityfrom the diode region by providing an index mismatch or index step.Accordingly, as shown, for example, in FIG. 1, the transparentinsulating layer 140 can provide an integral optical element for thereflective cathode contact 150, in addition to providing desiredelectrical insulation for the LED. Moreover, the transparent insulatinglayer 140 and the reflective cathode contact 150 can provide a hybridmirror.

An explanation of the operation of the transparent insulating layer 140as part of a hybrid reflector will now be provided. In particular, LEDstypically include multiple layers of different materials. As a result,light emitted from the active region must typically pass through oracross one or more of such layers before exiting the LED. Snell's lawdictates that the photons will be refracted as they pass from onematerial to the next. The angles at which the photons will be refractedwill depend upon the difference between the refractive indexes of thetwo materials and the angle of incidence at which the light strikes theinterface.

In an LED, although some reflected light will still escape the LED atsome other location, a certain percentage will be totally internallyreflected, never escape the LED, and will thus functionally reduce theexternal efficiency of the LED. Although the individual reduction in thepercentage of photons escaping may appear to be relatively small, thecumulative effect can be significant, and LEDs that are otherwise verysimilar can have distinctly different performance efficiencies resultingfrom even these small percentage losses.

Snell's law dictates that when light crosses an interface into a mediumwith a higher refractive index, the light bends towards the normal.Similarly, when light travels across an interface from a medium with ahigh refractive index to a medium with a lower refractive index, lightbends away from the normal. At an angle defined as the critical angle,light traveling from a medium with a high refractive index to a mediumwith a lower refractive index will be refracted at an angle of 90°;i.e., parallel to the boundary. At any angle greater than the criticalangle, an incident ray undergoes total internal reflection (TIR). Thecritical angle is thus a function of the ratio of the refractiveindexes. If the light hits the interface at any angle larger than thiscritical angle, the light will not pass through to the second medium atall. Instead, the interface reflects the light back into the firstmedium, a process known as total internal reflection. The loss of lightdue to this total internal reflection is known as the critical angleloss, and is another factor that reduces the external efficiency of theLED.

Embodiments of a hybrid mirror described herein use index mismatching toenhance total internal reflection (TIR) based on Snell's law. In orderto enhance TIR, it is desired to provide a large index change to a lowerrefractive index material relative to the GaN-based diode region. Thus,any light outside the escape cone angle given by Snell's law isinternally reflected back into the diode region, and can haveessentially no loss. The reflective cathode contact 150 and/or areflective anode contact can then be used to reflect the fraction of thelight impinging thereon from an omnidirectional light source.Accordingly, both the transparent insulating layer 150 and thereflective cathode contact act as a hybrid reflector according tovarious embodiments to enhance reflection of light emerging from thediode region back into the diode region.

Other embodiments of the invention can provide a reflective layer for avertical LED. Thus, light emitting diodes according to variousembodiments may also comprise a diode region including therein an n-typelayer and a p-type layer, and a contact for one of the n-type layer orthe p-type layer. The contact may comprise a transparent insulatinglayer 140 on the one of the n-type layer or the p-type layer that has anindex of refraction that is less than the one of the n-type layer or thep-type layer. A reflective layer 150 is provided that electricallycontacts the one of the n-type layer or the p-type layer, and thatextends on the transparent insulating layer. Accordingly, thetransparent insulating layer 140 can provide an integral optical elementfor a reflective layer 150 so as to provide a hybrid mirror that canimprove the reflectivity of the reflective layer 150 compared to absenceof the transparent insulating layer 140, because the transparentinsulating layer provides an index mismatch or index step to the dioderegion 110. In other embodiments, the reflective layer 150 can alsoelectrically contact, and in some embodiments ohmically contact, the oneof the n-type layer or the p-type layer, and may extend through thetransparent insulating layer 140 to make this contact. In still otherembodiments, a second contact may be provided for the other of then-type layer or the p-type layer. The second contact may comprise asecond reflective layer that ohmically contacts the other of the n-typelayer or the p-type layer. In other embodiments, the second contact maycomprise a transparent conductive layer that ohmically contacts theother of the n-type layer or the p-type layer, and the transparentinsulating layer 140 and the reflective layer 150 can both extend ontothe transparent conductive layer. These other embodiments will bedescribed in detail below, for example in connection with FIGS. 2 and 3.

Moreover, various embodiments as described herein can also provide adiode region 110 having first and second opposing faces 110 a, 110 b,and including therein an n-type layer 112 and a p-type layer 114. Areflective anode contact 130 ohmically contacts the p-type layer andextends on the first face 110 a. A reflective cathode contact 150ohmically contacts the n-type layer and extends on the first face. Thereflective anode contact 130 and the reflective cathode contact 150 areconfigured to reflect substantially all light that emerges from thefirst face 110 a back into the first face 110 a. Stated differently, thereflective cathode contact 150 can cover substantially all of the firstface 110 a that is outside the anode contact 130. Moreover, in otherembodiments, the reflective cathode contact 150 can also cover at leasta portion of the anode contact 130.

FIG. 2 is a cross-sectional view of an LED according to otherembodiments. In these embodiments, a reflective anode contact isprovided in addition to a reflective cathode contact.

More specifically, in FIG. 2, a diode region 110 is provided as wasdescribed in connection with FIG. 1. A substrate 120 is also provided,although it need not be provided in other embodiments. The substrate 120may be thinned relative to the thickness of the growth substrate. Areflective anode contact 130′ is provided that ohmically contacts thep-type layer 114 and extends on the first face 110 a. The reflectiveanode contact 130′ may include a two-layer structure including, forexample, about 5 Å of nickel (Ni) directly on the p-type layer 114 andabout 1000 Å of silver (Ag) on the nickel, to thereby provide an “NiAgmirror” 130′. The NiAg mirror 130′ can reflect at least 90% of thevisible light from the diode region 110 that impinges thereon. Otherreflective layers that also provide an ohmic contact to p-type galliumnitride may be used in other embodiments. It will be understood that thereflectivity of the NiAg mirror is determined primarily by the Agbecause only a very thin layer (in some embodiments less than about 10Å) of Ni is used. Moreover, when annealed, this nickel may convert tonickel oxide to enhance the ohmic contact for the Ag to the p-typegallium nitride. Thus, the NiAg mirror 130′ can have about the samereflectivity of Ag alone, but can provide a better contact and lowervoltage to the p-type layer. In other embodiments, pure Ag may be used.

Surrounding the NiAg mirror 130′ is a barrier layer 210 which mayinclude sublayers comprising about 1000 Å of titanium tungsten (TiW),about 500 Å of platinum (Pt) and about 1000 Å of titanium tungsten(TiW). The titanium tungsten/platinum sublayers may repeat in multiplerepetitions to provide a desired diffusion barrier. The diffusionbarrier layer 210 generally is not reflective. Thus, the face of theNiAg mirror 130′ that is directly on the p-type layer 114 provides areflective structure, but the barrier layer 210 that is on the sidewallof the NiAg mirror 130′ may not provide a reflective structure.

Continuing with the description of FIG. 2, a transparent insulatinglayer 140 is provided on the sidewalls of the via 118 and on the firstface 110 a outside the via 118. In some embodiments, as shown, thetransparent insulating layer 140 may also extend onto at least a portionof the NiAg mirror 130′. In some embodiments, the transparent insulatinglayer 140 may comprise about 0.5 μm of silicon diode (SiO₂). Thethickness of the SiO₂ may be configured to enhance the reflectivity fromthe reflective cathode contact 150, based on the operating wavelength ofthe LED and/or the index of refraction of the insulating layer, usingtechniques known to those skilled in the art. In particular, the silicondioxide may have an index of refraction of about 1.5, which is less thanthe index of refraction of gallium nitride (about 2.5), so that an indexmismatch or index step is provided by the transparent insulating layer140, which can actually enhance TIR from the diode region 110.

As also shown in FIG. 2, the reflective cathode contact 150 canohmically contact the n-type layer 112, for example on the floor of thevia 118 and can extend on the transparent insulating layer 140 on thesidewall of the via 118, and may also extend onto the transparentinsulating layer 140 that is outside the via 118 as indicated by 150 a.In some embodiments, the reflective cathode contact 150 may compriseabout 1500 Å of aluminum. Thicker reflective cathode contacts also maybe used. The hybrid reflector that includes the transparent insulatinglayer 140 and the aluminum reflective cathode contact 150 can reflect atleast 90% of the visible light from the diode region 110 that impingesthereon. In other embodiments, a separate ohmic contact layer 250 may beprovided between the reflective cathode contact 150 and the n-type layer112, to provide an ohmic contact to the n-type layer 112. In someembodiments, the ohmic contact layer 250 may comprise titanium, forexample annealed titanium, or aluminum/titanium alloy It will beunderstood that the ohmic contact layer 250 may be used in any and allof the embodiments described herein between the reflective contact 150and the n-type or p-type layer.

Finally, an anode pad 160 and a cathode pad 170 are provided. The anodepad 160 and the cathode pad 170 can include a stack of about 500 Åtitanium (Ti), about 2000 Å nickel (Ni) and about 1-3 μm of 80/20gold-tin (AuSn) alloy, to provide “TiNiAuSn pads”. Other materials maybe used, and not all of these layers may be used. For example, pure tinmay be used as it has a lower melting point. Moreover, in otherembodiments, a plating seed layer may be provided on the anode contactand on the reflective cathode contact, and at least a portion of theanode and/or cathode pads are plated on the seed layer. In still otherembodiments, the reflective cathode contact 150 and/or the barrier layer140 may provide the plating seed layer for plating the pads 160/170thereon. The plated anode and cathode pads can also provide mechanicalsupport and enhanced thermal efficiency.

Accordingly, embodiments of FIG. 2 may provide a reflective structure onthe first face 110 a that is configured to reflect substantially alllight, for example, at least 90% of the light that emerges from thefirst face 110 a back into the first face 110 a. In embodiments of FIG.2, the reflective structure comprises two different reflectors. Morespecifically, the reflective structure comprises a reflective surface ofthe anode contact 130′ that ohmically contacts the p-type layer 114, areflective surface of the cathode contact 150 that ohmically contactsthe n-type layer 118 and a reflective surface of extensions 150 a of thecathode contact 150 that extend between the reflective surface of theanode contact 130′ that ohmically contacts the p-type layer 114 and thereflective surface of the cathode contact 150 that ohmically contactsthe n-type layer 118, in combination with the transparent insulatinglayer 140. When viewed from the perspective of the diode region 110, allthe light that emerges from the diode region 110 into the anode andcathode contacts can be reflected back into the diode region except forlight that is absorbed by the barrier layer 210 on the sidewalls of theanode contact 130. Since the barrier layer 210 generally does not forman ohmic contact with the p-type layer 114, little or no light isgenerated in this region. Thus, there can be little or no light lossassociated with the barrier layer 210. Thus, from an area standpoint,the reflective structure of FIG. 2 can reflect the light that emergesfrom at least 85% of the area of the first face, and in someembodiments, at least 90% of the area. In other words, at least 90% ofthe diode face can be covered by mirror. Moreover, since the reflectivestructure can comprise nickel-silver (anode contact 130′) and aluminum(cathode contact 150), at least 90% of the light that impinges on thereflective structure may be reflected. In other words, the mirror mayhave at least 90% efficiency. Thus, in some embodiments, the onlyregions in the active light generating area on the p-type layer 114 notcovered by high reflectivity structures either have a dielectriccontact, and/or are reduced conductivity regions.

FIG. 3 is a cross-sectional view of other embodiments that employ atransparent anode contact. In particular, referring to FIG. 3, the anodecontact is a transparent anode contact 130″ that ohmically contacts thep-type layer 114 and extends on the first face 110 a. It will beunderstood that the transparent anode contact 130″ may extend to agreater or lesser extent than illustrated. In some embodiments, thetransparent ohmic contact for the p-type Group III-nitride layer 114 maybe a transparent conductive oxide, such as indium tin oxide (ITO) and,in some embodiments, may be about 2500 Å thick. The ITO may be at least90% transparent in the wavelengths of interest. It will be understoodthat the ITO may include other materials therein, such as nickel oraluminum. A current spreading layer 330, also referred to as “currentspreading fingers”, may be provided on a portion of the transparentanode contact 130″. The current spreading layer 330 may comprise, forexample, a sublayer of platinum (Pt) about 500 Å thick, a sublayer oftitanium (Ti) about 500 Å thick and a sublayer of gold (Au) about 0.5 μmthick, to provide a “Pt/Ti/Au” current spreading layer 330.

In embodiments of FIG. 3, the transparent insulating layer 140 extendsonto the transparent anode contact 130″ and the reflective cathodecontact 150 also extends onto the transparent insulating layer 140 thatis on the transparent anode contact 130″ as shown by 150 a. In someembodiments, as also shown in FIG. 3, the transparent insulating layer140 extends onto the transparent anode contact 130″ that is outside theportion on which the current spreading layer 330 is provided, and thereflective cathode contact 150 also extends onto the transparentinsulating layer 140 that is on the transparent anode contact 130″outside this portion. Thus, an integrated n-contact hybrid mirror isprovided that reflects light that passes through the transparent anodecontact 130″ back into the diode region 110. It will also be understoodthat in embodiments of FIG. 3, the ohmic contact layer 250 has beenomitted, so that reflective cathode contact 150 makes direct ohmiccontact with the n-type layer 112.

Accordingly, embodiments of FIG. 3 can provide a reflective structurethat comprises a reflective surface of the cathode contact 150 thatohmically contacts the n-type layer 112 and a reflective surface of anextension 150 a of the cathode contact 150 that extends onto thetransparent anode contact 130″, in combination with the transparentinsulating layer 140. From a total internal reflection standpoint, sincethe transparent anode contact 130″ also has a lower index of refractionthan the diode region (index of refraction of about 1.94 for ITO), theindex mismatch enhances TIR based on Snell's law. The transparentinsulating layer 140 that is on the transparent anode contact 130″ canfurther enhance TIR by providing an even lower index of refraction ofabout 1.5.

Thus, from the standpoint of reflection from the diode region 110, onlythe current spreading layer 330 may absorb light. Since the currentspreading layer is a small portion of the surface area of the firstface, embodiments of FIG. 3 may also provide a reflective structure thatreflects light that emerges from at least 90% of the area of the firstface, and in some embodiments, from at least 93% of the area of thefirst face. In other words, at least 90% of the diode face is covered bymirror. Moreover, the mirror may have at least 90% efficiency. It willalso be understood that the current spreading layer 330 on thetransparent anode contact 130″ may be less absorbing than the currentspreading layer 330 alone. In particular, due to the index of refractionchange at the ITO/GaN interface, the current spreading layer 330 may beless absorbing on an angle average basis than the current spreadinglayer 330 alone. This provides an additional benefit to using ITO as theN—GaN contact so that a metallic layer is not directly on thesemiconductor.

The potentially negative impact of the current spreading layer may alsobe reduced by reducing the light hitting the metal current spreadinglayer by quenching the p-GaN under the current spreading layer 330 sothat the light hitting that area mostly comes from an angle that isoutside the region directly under the current spreading layer 330. Thus,some embodiments can also incorporate a reduced conductivity region in ap-type layer that are congruent with nearby more opaque features, suchas the current spreading layer, as described in U.S. Patent ApplicationPublication No. 2008/0217635, the disclosure of which is herebyincorporated by reference in its entirety as if set forth fully herein.

Still referring to FIG. 3, an insulating layer 340, such as a secondlayer of silicon dioxide about 0.5 μm thick, may be provided on thereflective cathode contact 150. An anode pad 160 and a cathode pad 170may be provided to electrically connect to the current spreading layer330 and the reflective cathode contact 150, respectively. In embodimentsof FIG. 3, the insulating layer 340 may prevent the anode and cathodecontact pads 160 and 170 from short circuiting one another. In otherembodiments, however, the anode 160 and cathode 170 pads may be formeddirectly on the current spreading layer 330 and directly on thereflective cathode contact 150, and may be spaced apart so as to providea gap 172 therebetween, as was illustrated in FIG. 2, and as will bedescribed below in embodiments of FIG. 10. Many other configurations ofanode pads 160 and cathode pads 170 may be provided in otherembodiments.

FIG. 4 is a cross-sectional view of LEDs according to other embodiments.In particular, as was noted above, various configurations of anode pads160 and cathode pads 170 may be provided according to variousembodiments. In some of these configurations, a break in the reflectivecathode contact 150 may be desired, as shown in FIG. 4, so as to preventshort circuiting of the anode pad to the contact pad 170, and leave agap 172 therebetween. Unfortunately, due to the absence of thereflective cathode contact 150 in the gap, light in the gap may not bereflected back into the diode region 110. Embodiments of FIG. 4 canreduce or eliminate this problem by providing a reflective layer 450that is insulated from the anode pad 160 and/or the cathode pad 170, andthat extends across the gap 172. An additional (second) insulating layer440 may be provided to also insulate this reflective layer 450 from thediode region 110, if needed. Accordingly, a reflective layer 450 may beprovided in the gap 172, even though reflective cathode contact 150 hasa break across the gap 172.

FIGS. 5A and 5B are top views of anode pads 160 and cathode pads 170according to various embodiments. It will be understood, however, thatmany different configurations of anode pads 160 and cathode pads 170 maybe provided, depending on the desired external connections for thelateral LED.

FIG. 6 is a flowchart of operations that may be performed to fabricatelight emitting diodes according to various embodiments. In particular,at Block 610, a via, such as via 118, is etched through a p-type layer,such as a p-type layer 114, at a first face of a diode region, such as adiode region 110, to expose an n-type layer, such as an n-type layer112, therein. At Block 620, an anode contact, such as an anode contact130, 130′ and/or 130″, is formed on the first face that ohmicallycontacts the p-type layer. At Block 630, a transparent insulating layer,such as layer 140, is formed on the sidewalls of the via and extendingon to the first face outside the via. At Block 640, a reflective cathodecontact, such as a reflective cathode contact 150, is formed, thatohmically contacts the n-type layer on a floor of the via and extends onthe transparent layer that is on the sidewalls of the via, and on thetransparent layer that is on the first face outside the via. Pads, suchas anode pad 160 and cathode pad 170, may be formed at Block 650.Finally, if desired, the substrate may be removed or thinned at Block660. The substrate and/or the second face may be textured.

Embodiments of FIG. 6 may be generally used to fabricate variousembodiments described herein. Specific techniques may also be providedto fabricate specific embodiments. For example, embodiments of FIG. 3may be fabricated by etching the via 118 to expose the n-type layer 112at Block 610. A layer of indium tin oxide 130′ and a current spreadinglayer 330 may then be formed at Block 620. A layer of silicon dioxide,such as 0.5 μm of silicon dioxide, may be blanket deposited to providethe transparent insulating layer 140 at Block 630. A via may be etchedto expose the n-type layer 112 and aluminum may be blanket deposited toprovide the reflective cathode contact 150, leaving a gap over the ITOlayer 130″, at Block 640. TiNiAuSn pads 160 and 170 may be deposited atBlock 650. Other techniques may be used to fabricate other structuresaccording to various embodiments.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated.

FIGS. 7A and 7B are top and side cross-sectional views, respectively, ofLEDs according to still other embodiments. These embodiments may besimilar to embodiments of FIG. 2, except that a reflective seed layer750 is provided on the barrier layer 210 and is used as a plating seedfor plating the anode pad 160 and the cathode pad 170 thereon. Moreover,the ohmic cathode contact may be provided by a portion of the seed layerthat directly contacts the diode region 110 according to any of theabove-described embodiments. In these embodiments, the reflective seedlayer 750 may comprise successive layers of aluminum, titanium andcopper, while the pads 160 and 170 may comprise plated copper.

More specifically, embodiments of FIGS. 7A and 7B may be fabricated byfabricating the NiAg mirror 130′ to provide a p-type anode contact andby fabricating a barrier region 210 on the NiAg mirror 130′, as wasdescribed in connection with FIG. 2. The diode region 110 is then etchedto reach the n-type layer 112 (not illustrated in FIG. 7A or 7B), and toalso define the vias. A passivation layer 140 may then be deposited andetched to expose the n-type region on the floor of the via 118 and aportion of the barrier 210. A seed layer 750 may then be deposited,contacting the n-type region and the barrier. The anode pad 160 andcathode pad 170 are then plated on the seed layer 750 with aphoto-lithographically defined gap 172 (for example about 75 μm wide)between the anode and cathode pads. The portion of the seed layer 750 inthe gap 172 may then be etched such the extent of the remaining seedlayer is essentially the same as that of the anode pad and cathode pad.The gap 172 may then be filled with a gap filling layer 760, which maycomprise polyimide, for example. The silicon carbide substrate is thenremoved to produce the final structure of FIG. 7B.

Accordingly, embodiments of FIGS. 7A and 7B can provide an LED havingreflective anode contacts 130′, so that the entire surface is reflectiveexcept for where the barriers 210 on are directly on the diode region110. Thus, in embodiments of FIG. 7A, the entire structure has a mirror,except for the region immediately surrounding where the 16 vias 118 are.Moreover, in other embodiments, the seed layer 750 may comprise anon-reflective metal (for example, to provide improved ohmic contact tothe n-type layer 112) with only a small impact on the overall mirrorreflectivity since the light sees the seed layer only where the 16 vias118 are.

FIGS. 8A-8C are cross-sectional views of operations that may beperformed to remove the substrate 120 according to various embodiments.As shown in FIG. 8A, operations to fabricate the LED as were describedin connection with FIG. 7B may be performed on an LED epi 110 that is ona growth substrate 120. As shown in FIG. 8B, a carrier wafer 810, whichmay be semiconductor, glass and/or other conventional carrier wafer, isbonded to the plated anode pad 160 and cathode pad 170 using a glue 820or other bonding material/technique. In FIG. 8C, the substrate 820 isremoved, and the outer face of the diode region 110 is textured toprovide the structure of FIG. 7B.

FIG. 9 is a cross-sectional view of a light emitting diode according toyet other embodiments. In FIG. 9, a first transparent anode contact 130″and a current spreading layer 330 are provided, as was described inconnection with FIG. 3. However, in embodiments of FIG. 9, a transparentcathode contact 930 and current spreading layer 940 also may beprovided. The transparent cathode contact 930 ohmically contacts then-type layer 112 and extends on the first face 110 a. The extent of thetransparent anode contact 130′ and the transparent cathode contact 930may be more or less than that illustrated in FIG. 9. Moreover, thetransparent cathode contact 930 may comprise the same material as thetransparent anode contact 130″. For example, indium tin oxide may beused. In other embodiments, however, different transparent materials maybe used for the contacts 130″ and 930. In still other embodiments, thesame material may be used but may be deposited using differenttechniques and/or operating parameters. Similarly, the two currentspreading layers 330, 940, may be the same or different materials andmay be fabricated using the same or different processes.

Still referring to FIG. 9, a transparent insulating layer 140 isprovided that extends on the first face including on the transparentanode contact 130″ and on the transparent cathode contact 930. Areflective layer 150 is provided on the transparent insulating layerthat substantially covers the first face 110. The current spreadinglayer 330 may be provided between the transparent anode contact 130″ andthe reflective layer 150, and the current spreading layer 940 may beprovided between the transparent cathode contact 930 and the reflectivelayer 150. As was already described, the current spreading layers 330,940 may be different portions of the same layer. As also illustrated inFIG. 9, the reflective layer 150 may comprise first and second portionsof a layer that are connected to the respective current spreading layers330, 940.

Embodiments of FIG. 9 may provide a reflective layer 150 thatsubstantially covers the first face. Moreover, efficient lightextraction may be provided because the transparent anode contact 130″and the transparent cathode contact 930 may both comprise ITO that hasan index of refraction of about 1.9 and the transparent insulating layer140 may comprise a material, such as silicon dioxide that has an indexof refraction of about 1.5, which is lower than ITO. Moreover, when thediode region 110 is formed by Group III-nitrides, such as galliumnitride, having an index of refraction of about 2.5, the transparent ITOlayer 130″, 940 and the transparent insulating layer 140 may provide anindex mismatch or index step with the gallium nitride. Enhanced totalinternal reflection may thereby be provided by the stepped index hybridreflector compared to absence of the transparent insulating layer 140and the transparent ITO layers 130′, 940. Furthermore, the transparentsubstrate 120 may comprise transparent silicon carbide, which has anindex of refraction of about 2.6. Since the silicon carbide substrate120 need not be conducting, it may be of high resistivity and betransparent. Moreover, since the silicon carbide substrate 120 is indexmatched to the gallium nitride diode region 110 (i.e., about the sameindex of refraction), enhanced light extraction may be provided throughthe beveled sidewalls 120 a of the silicon carbide substrate. Thus, thetransparent silicon carbide substrate 120 can function as a lightextractor, as well as a mechanical and/or thermal substrate for the LED.

Finally, referring to FIG. 9, when the transparent anode contact and thetransparent cathode contact both comprise transparent conductive metaloxide, such as ITO, and the reflective layer 150 comprises an elementalmetal layer, such as aluminum, the first face 110 can be free of directcontact with elemental metal, whereas an elemental metal reflector 150can substantially cover the first face.

FIGS. 10A-10D and 10A′-10D′ are cross-sectional views and top planviews, respectively, of light emitting diodes according to yet otherembodiments during intermediate fabrication steps according to yet otherembodiments. These embodiments may only use one insulating layer,compared to embodiments of FIG. 3.

Referring to FIGS. 10A and 10A′, the diode region 110 including then-type layer 112 and p-type layer 114 are formed on a substrate 120. Ap-type ohmic contact is then formed. In FIGS. 10A and 10A′, atransparent p-type ohmic contact comprising ITO 130″ is formed. In otherembodiments, a metal mirror/ohmic contact such as NiAg may be formed. Inthis case, a barrier layer also may be formed, as was described above,to reduce or prevent silver migration.

Referring now to FIGS. 10B and 10B′, a p-current spreading layer 330 isthen formed when an ITO-type contact is used.

Referring now to FIGS. 10C and 10C′, silicon dioxide or anothertransparent insulating layer or combination of layers 140 is blanketdeposited, and then vias are opened to the n-type layer 112 and to thecurrent spreading layer 330.

Finally, referring to FIGS. 10D and 10D′, a layer of Al/Ti/Ni/AuSn isdeposited to form the anode and cathode contacts 160 and 170,respectively. It will be understood that it may be desirable for thetitanium and nickel layers to be appropriately thick to reduce orprevent mixing during reflow. Thicknesses of approximately 1000 Åtitanium and 1000 Å nickel may be used, in some embodiments. Moreover,gold tin may not be needed. Rather, the contact stack may be terminatedby gold to facilitate other solder attachment.

It will also be understood that, although one embodiment of a contactgeometry illustrated in FIGS. 10D, 10D′, other contact geometries may beprovided, as shown in FIG. 11. Yet other contact geometries may beprovided based on desired external connections.

FIG. 12 is a cross-sectional view of a light emitting diode of FIG. 3mounted on a mounting substrate in a flip-chip configuration accordingto various embodiments. It will also be understood that any of the otherembodiments described and/or illustrated herein may be mounted on amounting substrate in a flip-chip configuration.

Referring now to FIG. 12, a mounting substrate 1210, such as aninsulating mounting substrate comprising, for example, aluminum nitride(AlN), may be used to mount the LED of FIG. 3 thereon in a flip-chipconfiguration, such that the anode and cathode contacts 160 and 170 areadjacent the mounting substrate 1210 and the diode region 110 is remotefrom the mounting substrate 1210. Conductive traces 1216 and 1218 may beused to provide external connections for the diode. The conductivetraces 1216, 1218 may be electrically and thermally connected to thecontacts 160, 170 using solder or other die attach material 1220.Moreover, the area occupied by the cathode contact 170 may be enlarged,and in some embodiments maximized, whereas the area occupied by theanode contact 160 may be reduced, and in some embodiments minimized. Byproviding a large area for the cathode contact 170, the cathode contact170 may be directly electrically coupled to a grounded copper slug 1214or other heat sink material, to provide enhanced thermal efficiency forthe package. An intervening electrically insulating layer that couldreduce thermal efficiency is not needed.

In flip-chip mounting an LED as illustrated in FIG. 12, the provision ofa reflective structure, such as the reflective cathode contact 150 thatcovers substantially the entire first face of the diode, and isconfigured to reflect substantially all light that emerges from thefirst face back into the first face, may be exceedingly beneficial. Inparticular, in a flip-chip configuration, light that is not reflectedback towards the first face may be substantially lost, because themounting substrate 1210 may be substantially absorbing. Accordingly, toenhance and/or maximize light emission through the substrate 120 in aflip-chip configuration, it may be desirable to increase or maximize thearea of the first face that is covered by the mirror using variousembodiments described herein.

It will also be understood that other forms of mounting substrates, suchas metal core substrates, printed circuit boards, lead frames and/orother conventional mounting substrates, may be used to mount many of theembodiments described herein in a flip-chip configuration.

Additional discussion of various embodiments of the invention will nowbe provided. In particular, light emitting diodes according to someembodiments can provide a lateral flip-chip design. The substrate 120can form the emitting face of the diode, and may include lightextraction enhanced surfaces 120 d that include lenticular lenses orother enhancement features. Moreover, the substrate 120 includes beveledside edges 120 a. A reflective contact 150 can substantially cover thep-type layer. The reflector 150 can include multiple metal layers toincrease the range of frequencies reflected.

Compared to conventional vertical LEDs, lateral embodiments describedherein can provide contacts on the epitaxial layer that can be matedwith metals that offer greater reflectivity, such as aluminum. Moreover,when transparent silicon carbide is used as a device substrate, itstransparency can be defined by the resistivity range of the siliconcarbide. Specifically, in most cases, silicon carbide crystals thatcontain fewer dopant atoms, and thus have a higher resistivity, willexhibit greater transparency than silicon carbide crystals with moredopant atoms and higher conductivity. Vertical devices generally usehigher conductivity substrates. In vertical designs, the desired higherconductivity substrates tend to absorb more light and, thus, can reducethe external efficiency of the LED. Accordingly, many vertical designsmay remove all or part of the silicon carbide substrate.

In sharp contrast, lateral designs according to various embodiments, donot require conductive substrates. As a result, these lateral designscan incorporate more transparent (i.e., high resistivity) siliconcarbide substrates, while still demonstrating good forward voltagecharacteristics. For example, the resistivity of greater than 0.5 Ω-cm,and in some embodiments greater than 1 Ω-cm, may be provided. Thiscontrasts with vertical designs that may use a resistivity of betweenabout 0.08 Ω-cm to about 0.2 Ω-cm.

Various embodiments that were described herein can provide a reflectivestructure that is configured to reflect substantially all light thatemerges from the diode region back into the diode region. Such areflective structure may be extremely desirable for a flip-chip device,so as to reduce or prevent absorption of the emitted radiation by themounting substrate. In particular, various technologies are known toreduce absorption of light into a bond pad. For example, it is known toprovide reduced conductivity regions beneath a bond pad to reduce lightemission into a bond pad. It is also known to reduce light emission intoa bond pad by including an insulating layer beneath a portion of atransparent conductive bond pad. It is also known to use reflective bondpads, as described, for example, in U.S. Patent Application Publication2007/0145380, to reflect light that strikes the bond pad.

Embodiments described herein can provide far more than a reflective bondpad or reduced emission into a bond pad. Rather, some embodimentsdescribed herein can provide a reflective structure on the first face ofthe diode region that can be configured to reflect substantially alllight that emerges from the first face back into the first face.Accordingly, absorption by the mounting substrate can be reduced orminimized. In fact, in some embodiments, bond pad losses themselves maynot be significant, because the LED itself can have high extractionefficiency by reducing multiple passes due to total internal reflection.Accordingly, various embodiments described herein can do much more thanmerely mitigate the insignificant light loss from the bond pads.

Lateral designs can also provide more options for positioning a desiredmirror layer and the lateral design chips can be mounted with theepitaxial layers up or down. Specifically, the epitaxial layer can bemounted closest to the mounting structure with respect to the substrateor further from the mounting structure with respect to the substrate. Incircumstances where the epitaxial layers are placed on the mountingstructure (down), the mirror can be positioned on the epitaxial side ofthe overall device. Moreover, through-silicon via (TSV) technology, thatis widely used with large scale integrated circuit devices, can be usedin various embodiments herein to bond a wafer with light emitting diodesto a silicon wafer if desired. The silicon wafer can provide thesupporting structure when the silicon carbide substrate is ground to bevery thin (for example, less than about 50 μm of silicon carbide) orwhere the silicon carbide growth substrate is completely removed.Bonding pads may then be provided on the back of the TSV silicon wafer,substantially aligned to the contacts pads of the LED to provide amounting interface. The TSVs can connect the pads on the LED with thepads on the back of the silicon wafer.

Moreover, some embodiments as described herein can provide an integratedcontact stack that includes Al/Ti/Ni/AuSn, with thicknesses of theselayers according to some embodiments having been described above. Asalso described herein, the Al reflective layer can be separated from theTi/Ni/AuSn. Moreover, the actual bonding metal, for example AuSn, mayonly need to be thick enough to provide a good bond to whateversubstrate the LED will be mounted to. Thus, for metal depositionprocesses, the AuSn alloy may be sputtered, or sputtering and/or e-beamdeposition may be used to sputter individual AuSn layers. Someembodiments may use a thickness of between about 1 μm to about 3 μm but,in other embodiments, thicker layers may be used. Moreover, in someembodiments described above, copper may be thickly plated, for examplebetween about 20 μm and about 30 μm or even thicker, to providemechanical support.

Accordingly, some embodiments can provide bond pad metal integration, tothereby allow for large area bonding with relatively small gaps betweenthe pads. For example, gaps as small as about 30 μm or less between theAuSn anode and cathode layers may be used without undue concern aboutbridging. If the termination uses Au rather than AuSn, solders, pastes,preforms, etc. may be used, in which case it may be desirable to provideeither larger gaps between the contacts or reduced pad areas to bebonded. However, in some embodiments described herein, only flux may beneeded, and the alignment for dispensing may not be critical.

Accordingly, in some embodiments described herein, gaps between the dieattach surfaces may be reduced in size to the size of the gap betweenthe anode and cathode contacts. In some embodiments, a gap of less thanabout 75 μm may be provided and, in other embodiments, a gap of lessthan about 50 μm may be provided, which can provide excellent mechanicalintegrity and efficient heat dissipation. Accordingly, some embodimentsdescribed herein can provide an integrated reflective contact and heatsink, while allowing a small gap between the die attach surfaces. TheLED can then be flip-chip mounted to a submount, such as silicon,copper, aluminum and/or aluminum nitride with traces (for a leadframe-based package), directly onto a lead frame, or lead frame slug oronto a ceramic submount. Such mounting schemes can provide efficientthermal conduction paths away from the active layer.

Although some embodiments can provide advantages with respect to lateralLEDs, other embodiments can also enhance the external efficiency ofvertical LEDs. Moreover, the light enhancement designs of variousembodiments can offer additional advantages based upon the refractiveindex of silicon carbide. Specifically, the difference between therefractive index of silicon carbide and air, and between silicon carbideand most common encapsulants, is usually greater than the differencebetween the refractive index of other substrate materials (such assapphire) and air or encapsulants. As a result, silicon carbide tends toretract and internally reflect more light than do some other substratematerials. Because of that, enhancing the light output characteristicsof the surfaces of silicon carbide-based diodes can have aproportionally greater positive effect on the external quantumefficiency of these devices.

Accordingly, some embodiments may use transparent silicon carbide (indexof refraction of about 2.6) to extract light from the GaN-based dioderegion (index of refraction of about 2.5). Moreover, some embodimentsmay use ITO (index of refraction of about 1.9) and silicon dioxide(index of refraction of about 1.5) to couple between the GaN (index ofrefraction of about 2.5) and the reflective layer (such as aluminum).Accordingly, robust electrical, thermal and optical properties may beprovided.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1. A light emitting diode comprising: a diode region having first andsecond opposing faces and including therein an n-type layer and a p-typelayer; an anode contact that ohmically contacts the p-type layer andextends on the first face; a transparent insulating layer that extendson the first face outside the anode contact, with said transparentinsulating layer allowing at least 90 percent of the radiation impingingon it from said light emitting diode to emerge through it; and areflective cathode contact that electrically contacts the n-type layerand that extends through the transparent insulating layer and onto thetransparent insulating layer that is outside the anode contact, to coversubstantially all of the first face that is outside the anode contactwith the reflective cathode contact.
 2. A light emitting diode accordingto claim 1 wherein the transparent insulating layer also extends ontothe anode contact and wherein the reflective cathode contact alsoextends onto the transparent insulating layer that is on the anodecontact, to cover substantially all of the first face that is outsidethe anode contact with the reflective cathode contact, and to also coverat least a portion of the anode contact with the reflective cathodecontact.
 3. A light emitting diode according to claim 1 furthercomprising a via that extends into the first face to expose the n-typelayer, wherein the transparent insulating layer extends into the via andwherein the reflective cathode contact also extends on the transparentinsulating layer into the via to electrically contact the n-type layerthat is exposed in the via.
 4. A light emitting diode according to claim1 wherein the anode contact comprises a reflective anode contact thatohmically contacts the p-type layer and extends on the first face.
 5. Alight emitting diode according to claim 4 wherein the reflective anodecontact includes sidewalls, the light emitting diode further comprisinga barrier layer on the reflective node contact including on thesidewalls thereof.
 6. A light emitting diode according to claim 1wherein the anode contact comprises a transparent anode contact thatohmically contacts the p-type layer and extends on the first face.
 7. Alight emitting diode according to claim 6 further comprising a currentspreading layer on a portion of the transparent anode contact.
 8. Alight emitting diode according to claim 6 wherein the transparentinsulating layer extends onto the transparent anode contact and whereinthe reflective cathode contact also extends onto the transparentinsulating layer that is on the transparent anode contact, to cover atleast a portion of the transparent anode contact with the reflectivecathode contact.
 9. A light emitting diode according to claim 7 whereinthe transparent insulating layer extends onto the transparent anodecontact that is outside the portion and wherein the reflective cathodecontact also extends onto the transparent insulating layer that is onthe transparent anode contact outside the portion, to cover thetransparent anode contact that is outside the portion with thereflective cathode contact.
 10. A light emitting diode according toclaim 1 further comprising: an anode pad that is electrically connectedto the anode contact; and a cathode pad that is electrically connectedto the reflective cathode contact; the anode and cathode pads extendingon the first face in closely spaced apart relation to one another todefine a gap therebetween.
 11. A light emitting diode comprising: adiode region having first and second opposing faces and includingtherein an n-type layer and a p-type layer; an anode contact thatohmically contacts the p-type layer and extends on the first face; atransparent insulating layer that extends on the first face outside theanode contact; a reflective cathode contact that electrically contactsthe n-type layer and that extends through the transparent insulatinglayer and onto the transparent insulating layer that is outside theanode contact, to cover substantially all of the first face that isoutside the anode contact with the reflective cathode contact; an anodepad that is electrically connected to the anode contact; and a cathodepad that is electrically connected to the reflective cathode contact;the anode and cathode pads extending on the first face in closely spacedapart relation to one another to define a gap therebetween, the anodepad and the cathode pad both further extending on the reflective anodecontact and wherein the reflective anode contact includes a breaktherein corresponding to the gap; the light emitting diode furthercomprising a reflective layer that is insulated from the anode padand/or the cathode pad and that extends across the break.
 12. A lightemitting diode according to claim 10 further comprising a mountingsubstrate and wherein the light emitting diode is flip-chip mounted onthe mounting substrate such that the anode and cathode pads are adjacentthe mounting substrate and the diode region is remote from the mountingsubstrate.
 13. A light emitting diode according to claim 1 furthercomprising a transparent substrate on the second face.
 14. A lightemitting diode according to claim 13 wherein the transparent substrateincludes an outer face that is remote from the diode region, the outerface being differently textured in a first portion thereof than a secondportion thereof so as to provide an orientation indicator for the lightemitting diode.
 15. A light emitting diode according to claim 1: whereinthe diode region comprises a Group III-nitride; wherein the transparentinsulating layer comprises silicon dioxide; and wherein the reflectivecathode contact comprises aluminum.
 16. A light emitting diode accordingto claim 4: wherein the diode region comprises a Group III-nitride;wherein the transparent insulating layer comprises silicon dioxide;wherein the reflective cathode contact comprises aluminum; and whereinthe reflective anode contact comprises nickel and silver.
 17. A lightemitting diode according to claim 6: wherein the diode region comprisesa Group III-nitride; wherein the transparent insulating layer comprisessilicon dioxide; wherein the reflective cathode contact comprisesaluminum; and wherein the transparent anode contact comprises indium tinoxide.
 18. A light emitting diode according to claim 12: wherein thediode region comprises a Group III-nitride; wherein the transparentinsulating layer comprises silicon dioxide; wherein the reflectivecathode contact comprises aluminum; and wherein the transparentsubstrate comprises silicon carbide.
 19. A light emitting diodecomprising: a diode region having first and second opposing faces andincluding therein an n-type layer and a p-type layer; an anode contactthat ohmically contacts the p-type layer and extends on the first face;a transparent insulating layer that extends on the first face outsidethe anode contact; a reflective cathode contact that electricallycontacts the n-type layer and that extends through the transparentinsulating layer and onto the transparent insulating layer that isoutside the anode contact, to cover substantially all of the first facethat is outside the anode contact with the reflective cathode contact;an anode pad that is electrically connected to the anode contact; and acathode pad that is electrically connected to the reflective cathodecontact; the anode and cathode pads extending on the first face inclosely spaced apart relation to one another to define a gaptherebetween; wherein the reflective cathode contact also provides aplating seed layer for the anode and cathode pads and wherein the anodeand cathode pads are plated anode and cathode pads on the seed layer.20. A light emitting diode according to claim 1 wherein the reflectivecathode contact directly ohmically contacts the n-type layer.
 21. Alight emitting diode according to claim 1 further comprising an ohmiccontact that directly ohmically contacts the n-type layer, wherein thereflective cathode contact is on the ohmic contact.
 22. A light emittingdiode according to claim 21: wherein the diode region comprises GroupIII-nitride; wherein the transparent insulating layer comprises silicondioxide; wherein the ohmic contact comprises titanium; and wherein thereflective anode contact comprises nickel and silver.
 23. A lightemitting diode according to claim 16 further comprising a transparentsubstrate that comprises silicon carbide on the second face.
 24. A lightemitting diode according to claim 1 wherein the transparent insulatinglayer comprises a plurality of transparent sublayers.
 25. A lightemitting diode comprising: a diode region having first and secondopposing faces and including therein an n-type layer and a p-type layer;an anode contact that ohmically contacts the p-type layer and extends onthe first face; and a cathode contact that ohmically contacts the n-typelayer and also extends on the first face; wherein the anode contactand/or the cathode contact further comprise a reflective structure onthe first face that is configured to reflect substantially all lightthat emerges from the first face back into the first face, such thatsaid reflective structure reflects the light that emerges from at least90% of an area of the first face back into the first face.
 26. A lightemitting diode according to claim 25 wherein the reflective structure isconfigured to reflect at least 90% of the light that impinges thereonback into the first face.
 27. A light emitting diode according to claim25 wherein the reflective structure comprises a reflective surface ofthe anode contact that ohmically contacts the p-type layer, a reflectivesurface of the cathode contact and a reflective surface of an extensionof the cathode contact that extends between the reflective surface ofthe anode contact that ohmically contacts the p-type layer and thereflective surface of the cathode contact.
 28. A light emitting diodeaccording to claim 27 further comprising a barrier layer on the anodecontact including on sidewalls thereof, wherein the reflective structurereflects substantially all the light that emerges from the first faceback into the first face except for light that is absorbed by thebarrier layer on the sidewalls of the anode contact.
 29. A lightemitting diode according to claim 25 wherein the anode contact istransparent and wherein the reflective structure comprises a reflectivesurface of the cathode contact that ohmically contacts the n-type layerand a reflective surface of an extension of the cathode contact thatextends onto the transparent anode contact.
 30. A light emitting diodeaccording to claim 29 further comprising a current spreading layer onthe transparent anode contact, wherein the reflective structure reflectsall the light that emerges from the first face back into the first faceexcept for light that is absorbed by the current spreading layer on thetransparent anode contact.
 31. A light emitting diode according to claim25 further comprising: an anode pad that is electrically connected tothe anode contact; and a cathode pad that is electrically connected tothe reflective cathode contact; the anode and cathode pads extending onthe first face in closely spaced apart relation to one another to definea gap therebetween.
 32. A light emitting diode according to claim 31further comprising a mounting substrate and wherein the light emittingdiode is flip-chip mounted on the mounting substrate such that the anodeand cathode pads are adjacent the mounting substrate and the dioderegion is remote from the mounting substrate.
 33. A light emitting diodecomprising: a diode region having first and second opposing faces andincluding therein an n-type layer and a p-type layer; a reflective anodecontact that ohmically contacts the p-type layer and extends on thefirst face; and a reflective cathode contact that ohmically contacts then-type layer and that extends on the first face, wherein the reflectiveanode contact and the reflective cathode contact are configured tocollectively reflect at least 90% of all light that emerges from thefirst face back into the first face.
 34. A light emitting diodeaccording to claim 33 wherein the reflective anode contact comprises areflective layer that ohmically contacts the p-type layer and extends onthe first face, and a barrier layer on the reflective layer including onthe sidewalls thereof.
 35. A light emitting diode according to claim 33wherein the reflective cathode contact comprises: a transparentinsulating layer that extends on the first face outside the anodecontact; and a reflective layer that electrically contacts the n-typelayer and that extends through the transparent insulating layer and ontothe transparent insulating layer that is outside the anode contact. 36.A light emitting diode according to claim 35 wherein the transparentinsulating layer also extends onto the anode contact and wherein thereflective layer also extends onto the transparent insulating layer thatis on the anode contact.
 37. A light emitting diode according to claim35 further comprising a via that extends into the first face to exposethe n-type layer, wherein the transparent insulating layer extends intothe via and wherein the reflective layer also extends on the transparentinsulating layer into the via to electrically contact the n-type layerthat is exposed in the via.
 38. A light emitting diode comprising: adiode region having first and second opposing faces and includingtherein an n-type layer and a p-type layer; a transparent anode contactthat ohmically contacts the p-type layer and extends on the first face;a transparent cathode contact that ohmically contacts the n-type layerand that extends on the first face; a transparent insulating layer thatextends on the first face including on the transparent anode contact andthe transparent cathode contact; and a reflective layer that is on thetransparent insulating layer and that substantially covers the firstface; wherein each of said transparent contacts and said transparentlayer allow at least 90 percent of the radiation impinging on them fromsaid light emitting diode to emerge through them.
 39. A light emittingdiode comprising: a diode region having first and second opposing facesand including therein an n-type layer and a p-type layer; a transparentanode contact that ohmically contacts the p-type layer and extends onthe first face; a transparent cathode contact that ohmically contactsthe n-type layer and that extends on the first face; a transparentinsulating layer that extends on the first face including on thetransparent anode contact and the transparent cathode contact; areflective layer that is on the transparent insulating layer and thatsubstantially covers the first face; and a current spreading layerbetween the transparent anode contact and the reflective layer andbetween the transparent cathode contact and the reflective layer.
 40. Alight emitting diode according to claim 39 wherein the reflective layercomprises first and second portions, wherein the current spreading layerbetween the transparent anode contact and the reflective layerelectrically connects the transparent anode contact to the first portionand wherein the current spreading layer between the transparent cathodecontact and the reflective layer electrically connects the transparentcathode contact to the second portion.
 41. A light emitting diodeaccording to claim 38 wherein the transparent anode contact and thetransparent cathode contact both comprise indium tin oxide and whereinthe transparent insulating layer comprises material that has an index ofrefraction lower than indium tin oxide.
 42. A light emitting diodeaccording to claim 38 further comprising a transparent substrate on thesecond face that has an index of refraction that is about the same asthe diode region.
 43. A light emitting diode according to claim 38wherein the transparent anode contact and the transparent cathodecontact both comprise transparent conductive metal oxide and wherein thereflective layer comprises an elemental metal layer that is spaced apartfrom the first face such that the first face is free of direct contactwith elemental metal.